Flutrop CIRAD Avian Influenza

A simple model for simulating immunity rate dynamics in a tropical free-range poultry population after avian influenza vaccination
M. LESNOFF1*, M. PEYRE1 , P. C. DUARTE2, J.-F. RENARD1 AND J. C. MARINER2
Epidemiol. Infect., Page 1 of 9. f Cambridge University Press 2009
doi:10.1017/S0950268809002453 Printed in the United Kingdom
1 Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD),
Campus International de Baillarguet, Montpellier, France
2 International Livestock Research Institute (ILRI), Nairobi, Kenya
(Accepted 22 February 2009)

SUMMARY

In developing countries, vaccination against highly pathogenic avian influenza subtype H5N
(HPAI) in free-range poultry flocks is usually implemented as periodic campaigns and newborn
chicks are generally not vaccinated by farmers between vaccination passes. The demographic
population turnover leads to a continuous decrease in the population immunity rate (PIR) over
time. We present a simple Leslie matrix model for estimating population turnover and PIR
dynamics in a hypothetical small-size vaccinated free-range poultry population. Four different
vaccination scenarios were identified assuming necessary procedures to achieve immunity.
The results indicate that high levels of population immunity are difficult to sustain. Assuming an
animal immunity response of 80% after vaccination and a constant population size, PIR
4 months after vaccination was f30% in all the scenarios. Predictions averaged over time
showed mean PIR between 36% and 48%, which is below the population immunity thresholds
for eradication approximated from R0 estimates.

Key words: Avian influenza, free-range, Leslie model, population immunity rate, tropical poultry.

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